The Volbox will give you quick, inline 3.5mm audio volume control through a real knob. You can keep it in a spot that's easy to reach, or put it somewhere out of sight. To hook it up, just pass your audio through the female IN and OUT jacks. It can be used as a headphones volume control, with a laptop, TV, cell phone, tablet, radio, and basically anywhere there is an audio jack. It can also be used with aux jacks, line level signals, as an audio attenuator, or between two audio devices. Simple, functional, and built to last, the Volbox has been making people's life easier since 2015 with over 25,000 orders. It is built with quality parts to give you many years of reliable service. The case is made of ABS and it is held together with screws. Each Volbox is assembled by a person and every single part gets looked at for quality control. Measurements are 50mm x 35mm x 11mm tall (2" x 1 3/8" x 1/2"). The knob is 20mm x 12mm tall (3/4" x 1/2"). Note: This will NOT make the volume louder than the music player's maximum level. For that you would need an amplifier. No batteries are required. No cables are included. A brief instruction card is included and minimal packaging to help our beautiful planet. Please contact me through 鶹 at any time if you have questions about using the Volbox in your system and I will be happy to help you. Please remember, audio cables are not included. -Clark